<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<div id="app">
    <p>{{date}}</p>
</div>
<script src="vue.global.js">
    Vue.createApp({
        data(){
            return {
                date:'00:00:00'
            }
        },
        mounted(){
            setInterval(()=>{
                let d = new Date();
                this.data=d.getHours()+':'+d.getMinutes()+':'+d.getSeconds();
            },1000);
        }
    }).mount("#app")
</script>
</body>
</html>